1. Field of the Invention
The present invention relates to a rotary anode X-ray tube in which a rotating body is rotatably supported by means of dynamic pressure bearings on a fixed shaft supported on both sides thereof.
2. Description of the Related Art
In general, an X-ray tube device is used for a medical diagnosis system, an industrial diagnosis system, and the like. A rotary anode X-ray tube used in a medical diagnosis system is, as disclosed in Japanese Patent No. 3139873, operated in a severe use environment in which the tube is rotated at a high speed at a high temperature, and in a vacuum. In the X-ray tube disclosed in Japanese Patent No. 3139873, a fixed shaft is fixed on a cantilever-support member, a rotating body is fitted on the fixed shaft, and rotating body is rotatably supported by dynamic pressure bearings. The dynamic pressure bearings are provided between the rotating body and the fixed shaft with a liquid metal lubricant, wherein a liquid metal lubricant is applied in a gap between the inner surface of the rotating body and the outer surface of the fixed shaft to form the dynamic pressure bearing. The rotating body is rotated so that a dynamic pressure is generated in the liquid metal lubricant in the dynamic pressure bearings. Thus, the dynamic pressure stably supports the rotating body on the fixed body. By using the dynamic pressure bearings, it is possible to rotate the anode target at a high speed.
Further, reduction in size and weight is required of the X-ray tube and, in order to achieve the reduction in size and weight, it is necessary to cool the target through the liquid metal. In U.S. Pat. No. 5,541,975, there is disclosed an X-ray tube in which a fixed shaft is supported by a cantilever structure and a rotating body is rotatably supported on the fixed shaft by ball bearings. In this X-ray tube, the fixed shaft is formed into a hollow structure, a cooling pipe is inserted in the fixed shaft, a cooling liquid is supplied to the inside of the fixed shaft through the cooling pipe, and the fixed shaft is cooled by the cooling liquid so that the rotating body can be cooled.
Likewise, in JP-A H08-96889 (KOKAI), there is disclosed an X-ray tube in which a rotating body is rotatably supported on both sides of a fixed shaft with utilizing ball bearings. In this X-ray tube, the fixed shaft is formed into a cylindrical shape, and a cooling liquid is supplied in the inside space of the cylinder to cool a connector on the high-voltage side.
Furthermore, in U.S. Pat. No. 5,838,763, there is disclosed an X-ray tube in which a fixed shaft is supported at both ends thereof. In this X-ray tube, dynamic pressure bearings are provide between a rotating body and the fixed shaft wherein a liquid metal lubricant is applied to a gap between the inner surface of a rotating body and the outer surface of the fixed shaft. Furthermore, the fixed shaft is formed into a cylindrical shape, and a cooling liquid is supplied to the inside space of the cylinder, whereby the rotating body is cooled.
In the X-ray tube disclosed in Japanese Patent No. 3139873, heat is transmitted from the anode target to the fixed shaft which is supported by the cantilever structure, and heat is accumulated and held in the dynamic pressure bearings. Thus, there is the possibility of the bearing reaching a high temperature, and the possibility of the bearing capability being lowered. Accordingly, the structure of the X-ray tube disclosed in Japanese Patent No. 3139873 (KOKAI) is regarded as being unsuitable for reduction in size and weight.
The X-ray tube disclosed in U.S. Pat. No. 5,541,975 has a structure for cooling the connector on the high-voltage side, and the rotating body is constituted of a cylindrical body part on the bearing side, and a cylindrical body part supporting the anode target. In the rotating body, a space is formed between both the cylindrical body parts, thereby forming a structure in which heat from the anode target is hardly transmitted to the fixed shaft. Furthermore, the bearing is constituted of a ball bearing, the rotating body side of the duplicate cylindrical structure is in point contact with the fixed shaft, and hence there is the problem that heat generated at the anode target is hardly transmitted to the fixed shaft, and it is difficult to effectively cool the anode target and the rotating body.
In the X-ray tube disclosed in JP-A H08-96889 (KOKAI), the rotating body is supported with utilizing ball bearings. Although the fixed shaft supported by the cantilever structure can be cooled by the cooling liquid flowing through the inside thereof, the rotating body supporting the anode target is in contact with the fixed shaft through the ball bearing with which the rotating body is in point contact, and hence heat generated from the anode target is hardly transmitted to the fixed shat, thereby posing the problem that it is difficult to effectively cool the anode target and the rotating body.
In the X-ray tube disclosed in U.S. Pat. No. 5,838,763, the cooling liquid flows through the one-way flow path along the fixed shaft, and hence it is possible to increase the inflow/outflow amount, and enhance the cooling capability of the X-ray tube provided with the dynamic pressure bearings. However, the X-ray tube has a structure in which the center of gravity of the anode target is arranged outside the bearing portion, and thus the anode target is arranged between the bearing portion and the cathode. Accordingly, when the anode target having a large weight is rotated with slight eccentricity, there is the problem that the rotating body is easily vibrated, and moreover the reliability of the bearing portion is lowered.